The spine is critical in human physiology for mobility, support, and balance. The spine protects the nerves of the spinal cord, which convey commands from the brain to the rest of the body, and convey sensory information from the nerves below the neck to the brain. Even minor spinal injuries can be debilitating to the patient, and major spinal injuries can be catastrophic. The loss of the ability to bear weight or permit flexibility can immobilize the patient. Even in less severe cases, small irregularities in the spine can put pressure on the nerves connected to the spinal cord, causing devastating pain and loss of coordination.
Fusion is one method for treating the symptoms that can accompany a damaged spinal disc, or other spinal pathologies that can result in the impingement of neural structures. The primary goals of fusion procedures are generally to reposition (e.g. increase space and/or alignment between vertebrae) portions of the spine, decompressing impinged neural structures in the process, and to provide stability to maintaining the position of those vertebrae. Most commonly, a fusion procedure is performed by removing some or all of the disc material between the vertebral segments to be fused and depositing one or more interbody spacers into the disc space. Over time new bone grows across the disc space to provide a solid bridge between the vertebrae. As an alternative to fusion, other motion preserving implants can also be implanted in the disc space to reposition the vertebrae while still maintaining the ability of the vertebrae to move relative to each other.
In all of these procedures the ability to safely access the targeted portions of the spine and to effectively manipulate the instrumentation used to affect the work done on the spine is crucial to the success of the procedure. Traditionally, lumbar interbody fusion has been performed through procedures accessing the spine from the anterior (anterior lumbar interbody fusion (ALIF)) or posterior, (posterior lumbar interbody fusion (PLIF) and transforaminal lumbar interbody fusion (PLIF)) aspect of the patient. These procedures each present their own advantages and disadvantages. Posterior-access procedures, for example, involve traversing a shorter distance within the patient to establish the operative corridor and can be augmented with posterior fixation without requiring the patient to be flipped during the surgery, albeit at the price of stripping away or cutting back muscles, and having to reduce or cut away part of the posterior bony structures (i.e. lamina, facets, spinous process) in order to reach the target site, and presenting a relatively small access window within which to operate and advance an implant through. On the other hand anterior-access procedures do not involve stripping or cutting back muscles, or reducing or cutting away bony structures to reach the surgical target site, and also present a large access window, allowing for easier tool manipulation and the implantation of a larger, more stable interbody implant. However, they also require traversing through a much greater distance within the patient and mobilizing the abdominal contents, and sometimes the vascular structures running along the front of the spine, to establish the operative corridor.
In the last decade, advances in technology and technique have also made a lateral approach to the spine a popular alternative to anterior and posterior approaches. The lateral approach achieves many of the advantages of both the posterior and anterior approaches (e.g. avoids stripping or cutting of back muscles, abdominal contents, and vascular structures while presenting a large exposure through which a large implant can be advanced. On disadvantage with the lateral approach however is that the L5-S1 disc space, and sometimes the L4-L5 disc space cannot not be accessed due to the presence of the iliac crest. Thus, in many cases where multiple levels, including L5-S1 and/or L4-L5, are to be fused, the surgeon must choose between using the lateral approach on the upper level(s) and then flipping the patient in the middle of the surgery to perform an ALIF on the lower level(s), or foregoing the advantages that can accompany the lateral approach and doing each level through an anterior approach in order to avoid flipping the patient. The instruments and methods described herein are directed towards providing additional flexibility and options to the surgeon to eliminate, or at least reduce, these and other challenges.